Backing up with rsync

Rsync copies data to another directory, another disk volume, or
another machine. It only copies what needs to be copied; that is, if
a file hasn't changed since the last time you backed it up, rsync
won't bother copying it again. Even better, if only part of a large
file has changed, rsync only copies those bytes.

I don't see any point in calling rsync from Applescript, but if
you must, you can. I'd just write a Terminal bash script. For my
system, it looks like this: